Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$49.77	11.233%	$55.3607	$55.36	$55.35	$55.40
Purchase #2	$154.33	8.784%	$167.8863	$167.89	$167.90	$167.90
Purchase #3	$135.98	9.177%	$148.4589	$148.46	$148.45	$148.50
Purchase #4	$238.89	11.141%	$265.5047	$265.50	$265.50	$265.50
Purchase #5	$238.71	8.846%	$259.8263	$259.83	$259.85	$259.80
Purchase #6	$148.28	13.704%	$168.6003	$168.60	$168.60	$168.60
Purchase #7	$169.31	7.552%	$182.0963	$182.10	$182.10	$182.10
7 purchase totals =	$1,135.27		$1,247.7335	$1,247.74	$1,247.75	$1,247.80